1. Field of the Invention
The present invention relates to timing systems and controlled lighting systems, and particularly to a timer that supervises the automatic control of lighting by a photo-electric controller.
2. State of the Art
There are numerous applications today in which automatic control of lighting in a home is useful and desirable. For example, a common use of such control is to create the appearance that the house is occupied when in fact the residents are away on vacation. In a number of these applications, an electromechanical device or an electronic device is used to provide a switching action that connects a lamp to the a-c supply at one time and disconnects the lamp from the a-c supply at another time. In some such systems the switching action is initiated by a timer, and in other such actions the switching action is initiated by a light sensor.
The timed switching systems known to be available for the control of home lighting are designed to enable the user to "program" the times at which the lamp is switched on and off. In some devices, an analog input is provided for, with an analog display of the programmed time. In other devices, a digital keypad is provided for the entry of programmed times, and a digital display is provided. A common problem encountered in the use of all such devices is the complexity of the programming procedure. For many people, the programming procedure is too difficult to learn. For others, the procedure is too difficult to remember from one use of the device to another. Even those who can learn and remember how to use such a timing device often find it inconvenient to use because of the time required for the programming operation and the inconvenience of having to program the device several times during the year to match the changing times of dusk during the year. A common experience is for the resident of the house to think of the timer as he is preparing to leave the house, in a rush to depart on his vacation and already burdened with other last-minute concerns. Moreover, such systems do not provide automatic lighting on unusually cloudy days, for example, during daytime intervals when lighting is normally not required. Such failure to provide lighting when an occupied home might reasonably be expected to be lighted is a very undesirable feature of timed lighting control systems.
This difficulty can be overcome by the use of a photoelectric controller that automatically turns a lamp or other electric appliance on when the ambient light level has remained below a predetermined level for a predetermined length of time and automatically turns that lamp or other electric appliance off when the ambient light level has remained above a predetermined level for a predetermined length of time. A serious failing of available systems of this kind is that the lamp will remain turned on throughout the night. An improved version of such a system is now avaiable, in which an interval timer is provided to turn the lamp off after a predetermined length of time following the turning on of the lamp. It is ordinarily assumed that the lamp will be turned on at about dusk, and the interval timer is adjusted to turn off the lamp approximately five hours later, at a time at which the residents of the home might reasonably be expected to retire for the night. The presence of clouds or other obstructions of the sun during the daytime can cause the lamp to be switched on during the day, however. The use of an interval timer to turn the lamp off after a predetermined length of time can then result in the absence of lighting during hours of the day in which the residents of the home might reasonably be expected to be up and about and in need of artificial light if they were indeed at home. Such an occurrence represents a failure of the system, in that the home is not automatically lighted during normal waking hours as desired.
A second shortcoming of a photoelectric controller with an interval timer is that if an occupant of the home arises during the night after the timed interval has elapsed and turns on a light, that light may be sensed by the photoelectric timer as if it were daylight at the beginning of the next day. When the artificial light is turned off, the photoelectric controller then interprets the loss of light as an indication of nightfall and turns on the controlled lamp. In this way, a photoelectric controller can improperly cause a controlled lamp to be turned on during the night even though an interval timer is used.
The purpose of the present invention is to overcome the shortcomings of both the currently available timed switching systems and the currently available photoelectric controllers.